Medical imaging devices provide non-invasive methods to visualize the internal structure of a patient. Such non-invasive visualization methods can be helpful in treating patients for various ailments. For example, the early detection of cancer in a patient can be important in treating that patient. For most cancers, when detected at an early stage, the survival probability of the patient can increase.
There are many medical imaging methods available for visualizing the internal structure of a patient, each with its own benefits and its own limitations and while the examples and embodiments described herein relate to MRI systems, MRI scanners and MRI images, any displayed three-dimensional image can be dynamically transformed using the systems and methods described herein, for example a three-dimensional CT image, three-dimensional optical coherence tomography image, or other three-dimensional medical image of a tissue of a patient such as single photon emission computed tomography or positron emission tomography. Additionally, it will be appreciated there are many medical imaging methods that use a probe having a field of view and while the examples and embodiments described herein relate to ultrasound systems having a field of view, any medical imaging method having a field of view can be used in the systems and methods described herein, including OCT (optical) sensors and PET detectors.
Magnetic resonance imaging (MRI) is one such non-invasive medical imaging technique which uses magnetic fields to image tissue of a patient. A patient is placed inside a powerful uniform magnetic field of an MRI scanner, which can align the magnetic moments of protons in the tissue (typically hydrogen protons of water molecules in the tissue) in the direction of the field, precessing about the field at their Larmor frequency. An excitation magnetic field (typically orthogonal to the main magnetic field) near the Larmor frequency is applied to alter the alignment of the protons in the tissue, typically flipping the magnetic moment of the protons in the main field. When the excitation field is turned off, the protons emit a photon that can be detected and processed to form an MRI image of the tissue.
Ultrasound imaging, another non-invasive medical imaging technique, uses sound waves, typically produced by piezoelectric transducers to image a tissue in a patient. The ultrasound probe focuses the sound waves, typically producing an arc-shaped sound wave which travels into the body and is partially reflected from the layers between different tissues in the patient. The reflected sound wave is detected by the transducer and converted into electrical signals that can be processed by the ultrasound scanner to form an ultrasound image of the tissue.
Each of MRI imaging and ultrasound imaging has certain advantages and certain drawbacks. For example, ultrasound tends to provide improved imaging of tendon structure in a patient over the images of the same tendon structure provided by an MRI. Ultrasound tends to provide superior spatial resolution over similar images obtained by an MRI machine.
MRI imaging tends to provide superior soft-tissue contrast resolution as compared to ultrasound images, typical MRI images tending to allow individual structures such as a lung, liver, kidney, bowel, and gray and white matter to be distinguished. Additionally, ultrasound provides a smaller field-of-view as compared to MRI imaging, and the resolution of ultrasound images tends to be restricted by the sound wave penetration through soft tissues and bone. For example, ultrasound imaging has difficulty penetrating bone and thus typically only sees the outer surface of bone structure and not what lies within.
An advantage of ultrasound as compared to MRI imaging is that ultrasound imaging provides real-time feedback. For example, an ultrasound technician can position the ultrasound transducer directly on a patent in a first position and view the ultrasound image in real time. Subsequently, the technician can move the ultrasound transducer to a second, perhaps more desirable position, to view the new ultrasound image, again in real time. This ability too adjust the position of the transducer, while viewing the ultrasound image in real time, provides the technician the ability adjust the ultrasound image until they are satisfied with the displayed image. Real-time imaging can be helpful during biopsy, where the ultrasound transducer can be used to view an image of the biopsy tool in real-time, for example a biopsy needle as it is inserted in the tissue.
It would be advantageous to combine the advantages of MRI imaging (or any three-dimensional medical image such as single positron emission computed tomography, computed tomography, positron emission tomography, fluoroscopy or endoscopy) and ultrasound imaging, to view an image of a tissue in a patient simultaneously using multiple imaging techniques. By tracking the movement of an ultrasound probe and dynamically adjusting a MRI image (or any three-dimensional medical image), for example, to show the slice of the tissue in the MRI image currently being imaged by the ultrasound imaging device, a user is provided with two images of the same tissue at the same time, taking advantage of the benefits of multiple imaging techniques.